Computer generated hologram null compensator for optical metrology of a freeform surface

A computer-generated hologram (CGH) null compensator has been designed for optical metrology of a freeform surface (FFS) with positive base radius. The CGH is being employed in the freeform testing for the first time. The basic concept of the optical metrology and the testing procedure are explained explicitly. The design results of the CGH null compensator are presented in this article. Moreover, the design method and its results are discussed in detail.